Plant pests are a major factor in the loss of the world's important agricultural crops. About $8 billion are lost every year in the U.S. alone due to infestations of non-mammalian pests including insects. In addition to losses in field crops, insect pests are also a burden to vegetable and fruit growers, to producers of ornamental flowers, and to home gardeners.
Insect pests are mainly controlled by intensive applications of chemical pesticides, which are active through inhibition of insect growth, prevention of insect feeding or reproduction, or cause death. Good insect control can thus be reached, but these chemicals can sometimes also affect beneficial insects and may not be able to reach the site of infestation. Another problem resulting from the wide use of chemical pesticides is the appearance of resistant insect varieties. This has been partially alleviated by various resistance management practices, but there is an increasing need for alternative pest control agents.
Biological pest control agents, such as Bacillus thuringiensis strains expressing pesticidal polypeptides like delta (δ)-endotoxins (also called Cry proteins), have also been applied to crop plants with satisfactory results, thus offering an alternative or compliment to chemical pesticides. The genes coding for some of these Cry proteins have been isolated and their expression in heterologous hosts have been shown to provide another tool for the control of economically important insect pests. In particular, the expression of Cry proteins in transgenic plants has provided efficient protection against certain insect pests, and transgenic plants expressing such proteins have been commercialized, allowing farmers to reduce or eliminate applications of chemical insect control agents.
Other, non-endotoxin genes and the proteins they encode have also been identified. U.S. Pat. Nos. 5,877,012, 6,107,279, 6,137,033, and 6,291,156, as well as Estruch et al. (1996, Proc. Natl. Acad. Sci. 93:5389-5394) and Yu et al. (1997, Appl. Environ. Microbiol. 63:532-536), all herein incorporated by reference, describe a new class of insecticidal proteins called Vip3. Vip3 coding sequences encode approximately 88 kDa proteins that are produced and secreted by B. thuringiensis during its vegetative stage of growth (vegetative insecticidal proteins or Vip). The Vip3A protein possesses insecticidal activity against a wide spectrum of lepidopteran pests, including, but not limited to, black cutworm (BCW, Agrotis ipsilon), fall armyworm (FAW, Spodoptera frugiperda), tobacco budworm (TBW, Heliothis virescens), and corn earworm (CEW, Helicoverpa zea), but has no activity against the European corn borer (ECB, Ostrinia nubilalis). More recently, plants expressing the Vip3A protein have been found to be resistant to feeding damage caused by hemipteran insect pests (U.S. Pat. No. 6,429,360). Thus, the Vip3A protein displays a unique spectrum of insecticidal activities. WO03/075655, WO02/078437, WO 98/18932, WO 98/33991, WO 98/00546, and WO 99/57282, have identified other members of the Vip3 class of proteins.
One concern raised regarding the deployment of transgenic crops expressing insecticidal proteins is whether insect pests will become resistant to the insecticidal proteins. The seed industry, university researchers and the US Environmental Protection Agency have worked together to develop management plans to help mitigate the onset of insect resistance. These plans are based primarily on a high dose and refuge strategy. A high dose strategy for European corn borer in corn, for example, is to use corn hybrids that express high enough levels of an insecticidal protein to kill even partially resistant European corn borers. The underlying hypothesis is that killing partially resistant ECB and preventing their mating greatly delays the development of resistance. The success of a high dose strategy depends in part on the specific activity of the insecticidal protein to European corn borer and how much of that protein can be expressed in the transgenic corn plant. For example, the higher the specific activity of an insecticidal protein to a pest, less of the insecticidal protein is required to be expressed in a transgenic plant to achieve a high dose strategy. Thus, for example, because the Cry protein, Cry1Ab, is very toxic to European corn borer larvae (i.e. high specific activity), the levels of expression of Cry1Ab that are achievable in transgenic plants easily places such corn hybrids in a high dose category.
Therefore, there remains a need to discover new and effective pest control agents that provide an economic benefit to farmers and that are environmentally acceptable. Particularly needed are control agents that are targeted to a wider spectrum of economically important insect pests and that have a high specific activity against insect pests that are or could become resistant to existing insect control agents. Furthermore, agents whose application minimizes the burden on the environment are desirable.
Accordingly, the invention addresses the previous shortcomings in the art by providing compositions comprising Vip polypeptides having altered pesticidal (e.g., insecticidal) activity against a target organism (e.g., an insect) and/or altered levels/degrees of toxicity toward any particular cell and/or organism as well as methods for making and using such polypeptides.